I'm not 100% certain, but my first pass at this would be querying against the definition field in the sys.all_sql_modules view in the DB in question. Something like:

select ao.name

, asm.object_id

, asm.definition

from sys.all_sql_modules asm

inner join sys.all_objects ao on asm.object_id = ao.object_id

where asm.definition like '%usp_SignOFF_Count%'